Magnetic drives such as hard disk drives (HDD) are used in almost all computer system operations. In fact, most computing systems are not operational without some type of hard disk drive to store the most basic computing information such as the boot operation, the operating system, the applications, and the like. In general, the hard disk drive is a device which may or may not be removable, but without which the computing system will generally not operate.
The basic hard disk drive model was established approximately 50 years ago and resembles a phonograph. That is, the hard drive model includes a storage disk or hard disk that spins at a standard rotational speed. An actuator arm with a suspended slider is utilized to reach out over the disk. The arm carries a head assembly that has a magnetic read/write transducer or head for reading/writing information to or from a location on the disk. The complete head assembly, e.g., the suspension and head, is called a head gimbal assembly (HGA).
In operation, the hard disk is rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are tracks evenly spaced at known intervals across the disk. When a request for a read of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head writes the information to the disk.
Over the years, the disk and the head have undergone great reductions in their size and the disk has seen significant increase in its recording density. Much of the refinement has been driven by consumer demand for smaller and more portable hard drives such as those used in personal digital assistants (PDAs), MP3 players, and the like. For example, the original hard disk drive had a disk diameter of 24 inches with a recording density <1 Megabits/in2 (Mb/in2). Modern hard disk drives are much smaller and include disk diameters of less than 2.5 inches (micro drives are significantly smaller than that) with recording densities >100 Gigabits/in2. Advances in magnetic recording are also primary reasons for the reduction in size.
The increase of recording density has been achieved through the dramatic increase in both of the recording linear density, kilobits per inch (KBPI), and the track density kilo-tracks per inch (KTPI). In general, an increase of linear density type means recorded bits have to be packed in dense configuration along the circumferential direction on a track written on the disk. Error rate can be significantly degraded by the increase of linear density.
An increase of the track density type implies that the recorded tracks along the radial direction of a disk are packed closer together. When the written tracks are packed closer together, not only does the error rate performance of a written track degrade but also the adjacent track interference (ATI) will become a severe problem. In general, ATI occurs when old information stored in the adjacent tracks (typically the two neighboring tracks on either side) of the data track being written become degraded after many repetitive writings to the data track. For example, as shown in Prior Art FIG. 1, a read-write head 105 has a fringe field 110 (or writing bubble) associated with the write process. In general, when the head 105 is writing to track n on disk 120, a portion of the fringe field 110 overlaps onto tracks n+1 and n−1. This overlap will result in added noise and degradation of the data on the tracks n+1 and n−1.
With reference now to Prior Art FIG. 2, the fringe field effect can also be more problematic at the inner diameter (ID) 210 and outer diameter (OD) 220 of the disk 120 where the read and write head mounted on the actuator 230 is not symmetric with respect to the disk track but is skewed (e.g., at an angle) with respect to the track. In general, the skew provides additional and variable loss rates per adjacent tracks of the disk 120 depending on the location of the actuator 230, e.g., ID 210, middle 215, or OD 220.
Presently, there are two main methods to overcome the ATI issue. The first method is to reduce the size of the head 105, thereby reducing the size of the fringe field 110. However, as is well known in the art, the reduction of the size of head 105 results in an increased error loss rate in the recording system. The second method is to stop decreasing the track pitch (or width). However, maintaining the track at a fixed pitch significantly impacts the capability to increase storage capacity on the magnetic storage device.